Dropping device

ABSTRACT

The present invention relates to a dropping device, preferably borne by a carrier aircraft, for distributing interference medium and especially electronic raspberry. The device according to the invention represents in principle an improvement to the device known through SE 8302508-0 and it is characterized firstly in that it has been provided with separately rotatable accelerator shafts ( 14, 15 ), which have the dual function firstly of acting as locks for an unwanted feed-out of interference medium packs ( 4 ) and secondly, when a feed-out has been activated, of executing this and giving the fed-out interference medium pack ( 4′ ) an increased feed-out speed, partly due to the device having been provided with a totally new, specially configured indexing mechanism.

The present invention relates to a dropping device, preferably borne bya carrier aircraft, for distributing interference medium and especiallyelectronic raspberry and interference medium with infrared (IR)signature, comprising a magazine provided with a rear feed-out openingviewed in the flight direction of the carrier aircraft and a number ofpacks of interference medium which are arranged one behind the other inthe magazine and can be fed out on command, one-by-one through thefeed-out opening, by a feed-out device forming part of the saidmagazine.

The basic principles for such a dropping device are previously knownthrough, for example, SE B 8302508-0, whilst various types ofinterference medium packs suited thereto are described in EP 0 278 568and SE B 505 070.

The dropping device described in SE B 8302508-0 is also thereforeincluded, in which a magazine provided with a rear fed-out openingviewed in the flight direction of the carrier aircraft and within whichpacks of interference medium, arranged one behind the other, can be fedrearwards step-by-step towards and out of the feed-out opening by a feedram driven by two parallel-running drive belts fastened to the front andrear edge of the ram, which drive belts firstly run along opposite sidesof the magazine, on both sides of the packs of interference mediumdisposed therein, and secondly run back over diverting wheels disposedin the front and rear part respectively of the magazine, whereby theyform closed loops. The said front diverting wheels are further joined bygearwheels one to another and to the motor which drives the whole of thefeed-out system. The rear diverting wheels are then driven, in turn, bythe feed belts. Level with the feed-out opening, special gearwheels aredisposed on the same shafts as the rear diverting wheels and drivenparallel with these, which special gearwheels, by interacting withtoothed members on the packs, firstly, as long as they are stationary,act as stop catches for the rearmost packing and secondly, when rotatedby a feed step, act as feed-out members for the same pack and finally,in connection with the feed-out of the rearmost pack, also separate thelatter from the following pack with which in the original position it ismeant to be coupled.

The above-described device has been widely used within a number ofairforces throughout the world and has there proved both reliable andfunctional. A potential risk which has recently been observed is howeverthat if both drive belts fail then the dropping device could in thisrealization end up releasing its entire load of packs ofinterference-suppression medium in a single sweep and this also withoutcommand. This theoretical possibility is in fact built into the system,since it is the gearwheels which act as both locks and feed-out membersand these will be totally without both locking and driving function inthe event of a double belt rupture. Like most other constructions whichexist, neither is the device according to SE B 8302508-0 so good that itcannot also be improved and the present invention now relates to amodified variant of this device, which firstly provides a higherfeed-out speed for the packs in question and secondly comprises a newindexing or drive function for the feed belts, i.e. de facto the feedram and the packs of interference medium. In its new modified variant,the device also has the advantage that no feed-out whatsoever can occurunless the drive motor of the dropping device is working.

The higher feed-out speed for the packs of interference medium has beenachieved according to the invention by the fact that the gearwheels ofthe older construction which co-rotate with the feed belts have beenreplaced by accelerator shafts or cam shafts which are arrangedseparately mounted in the side edges of the magazine feed-out openingand which, though parallel with the rear diverting wheel shafts of thedrive belts, have had their motion stepped up by a number of wholemultiples relative to the said diverting wheel shafts and are providedwith the same number of brake and separation/acceleration cams whichcorresponds to that part of a turn by which it has to rotate in order toexecute a feed-out of a pack of interference medium.

The accelerator shafts or cam shafts are configured with brake andseparation/acceleration cams, which have the function firstly ofblocking the feed-out of packs when no feed-out is to occur and secondlyof exposing the feed-out opening when the feed-out is started andadditionally of separating the outermost pack from its originaldetachable union with the next pack and finally of giving the outermostpack a final accelerating shove away from the dropping device.

As indicated previously, the feed-out device according to the inventionalso comprises a safety function which prevents any form of involuntaryfeed-out of interference medium packs after a drive belt rupture. Thissafety function has been achieved by the accelerator shafts in theflight direction of the carrier being made self-locking with respect tothe interference medium packs. In the rest position of the device, theoutermost interference medium pack in the feed-out direction will infact always come to bear with its feed lugs disposed on both sides ofthe same against part-cylindrical locking surfaces on the acceleratorshafts. These locking surfaces in turn constitute the outer periphery ofone or other of the cams of the respective accelerator shaft. Betweenthese part-cylindrical locking surfaces the accelerator shafts are thenprovided with their special feed grooves, which, when the acceleratorshaft is rotated by the dedicated drive function, enter into engagementwith the feed lug on the interference medium pack which is next in lineto be fed out.

The dropping device according to the invention also requires a reliableindexing mechanism. The indexing mechanism which has now been developedfor the dropping device according to the invention has a number ofadvantages which make it particularly well suited for use under theconditions for which the dropping device is intended and the specialstresses to which it might herein be exposed, yet the indexing mechanismin question is also at the same time more universally applicable, forexample in automatic packaging machines and other devices requiring areliable, step-by-step and continually repeated feed function.

The indexing mechanism in question is thus dynamically balanced, whichmakes it independent of external vibrational and gravitationalinfluence, which is essential when it is a question of parts belongingto modern combat aircraft. It further requires very little space totransmit high torques. It has high repeatability and, by virtue of thefact that indexing is effected through mechanical connection of inprinciple a single part, its indexing is independent of the friction forforce/torque transmission.

The working of the indexing mechanism in question incorporates thefeature that one or more turns of the rotation of an input shaft is/arerelayed as indexing to a second output shaft. By choosing the number ofturns which are required to be extracted from the output shaft, a numberof different indexings can therefore be obtained. This gives theindexing mechanism in question a very high degree of flexibility.

The step-by-step feeding or indexing is thus achieved according to theinvention by mechanical connection between a rotary input motor shaftand a driver, which is in turn is connected to a second output shaft,which is in line with the motor shaft but totally detached therefrom,and this second output shaft, following connection, imitating therotation of the motor shaft for one or more full turns, wholly dependentupon the setting, so as thereafter to be disconnected and braked withimmediate effect. According to a preferred embodiment of this system,the motor shaft is directly connected to a cylindrical drive drumarranged concentrically about the same, which drive drum is providedinternally with a fluting in the form of grooves or cavities againstwhich a driver which is adjustable between two different positions canbe connected and disconnected. In its normal position, the driver, whichis thus connected to the second output shaft, is held by an eccentric inengagement with a system-fixed stop lug. As soon as the eccentric isreadjusted so that its influence upon the driver ceases, the driver willenter into engagement position against the flutes of the drive drum andwill accompany the latter for one or more full turns so as, as soon asthe latter re-establishes contact with the eccentric, to be disconnectedfrom the drive drum and with its opposite end enter into engagement withthe stop lug, whereupon the stop lug itself and the output shaft aresimultaneously sharply braked. The sole control function which isrequired in this system, over and above the purely mechanical control ofthe connection and disconnection of the eccentric, is a delay betweenthe activation command and the connection of the driver, which gives themotor time to reach full speed before the driver is coupled togetherwith the drive drum. In those cases in which the drive motor is alwaysswitched on, there is obviously no need for any delay whatsoever. It isadditionally required that the eccentric shall have been returned to itsoriginal position before the driver has completed the intended number ofturns.

The driver which is characteristic of the device according to theinvention is mounted tiltably about a crankshaft arranged parallel withthe output shaft and somewhat eccentrically relative to the same, whilstthe driver itself extends at a tangent transversely to this shaft, aboutwhich it is tiltable between its two working positions, i.e.alternatively with its end edge facing towards the rotational directionof the motor and in bearing contact against the fluted inner side of thedrive drum or with its end edge facing in the rotational direction ofthe motor and in bearing contact against the fixedly disposed brake lug.In order to tilt over the driver from its position in bearing contactagainst the fluted inner side of the drive drum, in which position itcan be held by, for example, a spring, into its other locked position inwhich its other end bears against the brake lug, the aforementionedmechanically adjustable eccentric, disposed in a fixed mounting directlybeyond the outer edge of the drive drum, can preferably be used, bymeans of which the driver can be forced over into its other position.For this, the eccentric quite simply lifts the particular end of thedriver out of its engagement with the fluting of the drive drum,whereupon the front end of the driver in the rotational directionencounters the stop lug. The fact that the eccentric has a fixedlydisposed mounting and the drive drum and the driver, when the latter isconnected, rotate about the shafts in question, means that the driverand the eccentric have one contact possibility per turn.

The invention has been defined in the subsequent patent claims and inwhich it should be noted that the indexing mechanism to which referencehas previously been made can also be used in connection with otherdevices in which a similar step-by-step operation is desirable.

The invention shall now be somewhat further described in connection withthe appended drawings, in which:

FIG. 1 shows the basic principles for the dropping device according tothe invention

FIGS. 2-4 shows in larger scale a detailed picture of the feed-outfunction

FIG. 5 shows a section through the indexing function

FIGS. 6-9 shows the main parts of the indexing function and

FIG. 10 shows the main parts of the indexing function in brakedposition, and

FIG. 11 shows the main parts of the indexing function once indexing hasstarted.

As can be seen from FIG. 1, the basic layout for the dropping deviceaccording to the invention thus comprises a magazine 1 in which there isdisposed a displaceable feed ram 2 provided with an integrated resilientfront ram plate 3. In the direction of feed of the ram, ahead of thesame, there are a number of packs 4 of interference medium. The packsare in the magazine preferably coupled together to form a unit, but theycan relatively easily be disconnected from one another. The motion ofthe feed ram 2 is controlled and directed by two feed belts 5,6, one oneach side of the magazine. The feed belts 5,6 are fixed at their ends inthe front and rear edge respectively of the ram and the belt loops whichare thus obtained run over diverting rollers 7,8 and 9,10 disposed inthe front and rear edge respectively of the dropping device. Twotensioning rollers 11,12 are also included. The rear diverting rollers9,10 in the flight direction of the carrier are connected to an indexingfunction, by means of which the feed belts 5,6 and hence also the ram 2and the packs 4 can be displaced within and out of the magazine. In therear edge of the dropping device, this is configured with a feed-outopening 13. The flight direction of the carrier aircraft is indicated inthe figure by the arrow F. The feeding of the packs 4 within themagazine is therefore effected rearwards in the flight direction.

On each side of the feed-out opening 13 of the magazine 1 there areadditionally found accelerator shafts or cam shafts 14, 15, which, viagear units 16, 17, are driven by the diverting rollers 9,10 but athigher speed.

In a dropping device configured according to the example shown,{fraction (1/12)} of a turn is required on the diverting rollers 9,10 tofeed out a pack of interference material. At the same time theaccelerator shafts or cam shafts 14,15 pass through ⅓ of a turn, i.e. ata speed which is 4 times as high.

The working of the accelerator shafts or cam shafts 14,15 can be seenfrom FIGS. 2-4, of which FIG. 2 shows the starting position in which thefirst cam 18 of the cam shaft 14 blocks the feed-out of the containers4′ and 4″. As can be seen from FIGS. 2-4, the containers 4′ and 4″ areprovided with special feed-out lugs 19 and 20 having flanks 21 and 22which are obliquely bevelled rearwards in the feed-out direction. In itslocked stop position, the outermost pack 4′ bears with the obliquelybevelled flank 21 of its stop lug 19 against the part-cylindrical outerperiphery 23 of the accelerator shaft or cam shaft 14. In this position,the device is therefore locked in self-locking arrangement. When the camshaft 14 starts to move in the direction of the arrow B, the cam 18first allows the pack 4′ to move forward in that its feed lug 19 canenter into the space between the first cam 18 of the cam shaft 14 andits second cam 24, whereafter the front edge 25 of the cam 24 entersinto engagement with the top corner 26 of the feed lug 19 at the sametime as its part-cylindrical flank 27 stops the feed lug 20 of thecontainer 4″ in that the obliquely bevelled flank 22 of the said feedlug comes to bear against the same. The result is that the container 4″is stopped at the same time as the container 4′ is prized loose from thesame and is given an extra shove in the feed-out direction, which isflown per se in FIG. 4, after which the accelerator shaft or cam shaft14 is sharply braked in the position shown in FIG. 2 but with the cam 24as the braking cam and with the container 4″ in the position for thenext feed-out.

The cam shafts 14,15 thus operate at the same time as the entirequantity of packs 4 is fed towards the feed-out opening 13 (see FIG. 1)but the cam shafts operate considerably faster. The specificconfiguration of the cam shafts 14 and 15 with the part-cylindricalflanks 27 of the feed cams and the interaction of these flanks with thefeed lugs 19,20 of the packs 4 have allowed the drive system to be givenself-locking properties.

Compared with an older dropping device configured according to SE B8302508-0, the feed-out speed has been able in principle to be doubled,which is vitally important since this provides a considerably fasterdistribution of the interference medium in the pack.

In order to enable the above-described device to work perfectlysatisfactorily, there is a need for very precise indexing or advancementby the diverting wheels 9,10, from which all functions emanate by virtueof the fact that they are coupled there via direct-acting gear units.

The indexing mechanism referred to here shall now be described ingreater detail in connection with FIGS. 5-11.

Directly connected to the drive shaft 28 for an electric motor there isa drive drum 29. This has an internal cylindrical surface 30 providedwith a considerable number of “cavities” 31 separated by banks 32.

Also forming part of the indexing mechanism is a driver 33, which isconnected via a continuous shaft hole 34 to a driver disc 35 by acylindrical shaft 36 secured in the latter. The driver disc 35 has anoutput shaft 37, which lies in line with the shaft 28 but which isdetached therefrom. The driver 33 has a drive edge 38, which, in themounted state, faces towards the cavities 31 of the drive drum 29, and abrake edge 39 facing in the opposite direction.

Between the drive drum 29 and the driver disc 35 there is furtherdisposed an immovable brake calliper 40. As can be seen from FIG. 10,this has a brake lug 41 against which the driver 33 can be brought tobear by an eccentric 42 likewise disposed between the drive drum 29 andthe driver disc 35. The driver 33 is provided internally with a spring(not visible in the figures), which endeavours to rotate it about theshaft 36 in the direction of the arrow E.

The eccentric 42 is adjustable by means of a link 44 and a control lever45 between the original rest position shown in FIG. 10 and the startposition shown in FIG. 11.

Whenever a container of interference medium is fed out, the motor whichdrives the feed drum 29 is started and once the motor has reached fullworking speed in the direction of the arrow M the control lever 45 isactuated in the direction of the arrow S, whereupon the eccentric 42releases its grip against the driver 33, the drive edge 38 of the latterbeing brought by the spring (not shown in the figure) into contact withthe nearest cavity/cam 31/32 in the drive drum 29 and the driver 33taking the driver disc 35 and the shaft 37 along with it in its hereuponcommenced rotary motion. As soon as the eccentric 42 has let the driver33 pass, it will be returned to its original position if indexing ofjust one turn is required, which means that as soon as the driver 33 hascompleted a turn it will slide up onto the eccentric 42 and will hencebe disconnected from the drive drum 29 at the same time as its brakeedge 39 is brought to bear against the brake edge 41 of the brakecalliper 40 which produces a direct rotational halt for the shaft 37.

This device thus provides very precise indexing which always yields oneor more full feed turns. This precise indexing in the form of one ormore feed turns can then be converted via a direct-acting gear unit toany form of desired feed motion which is required for each individualfunction.

I claim:
 1. An airborne dropping device for distributing interferencemedium including electronic raspberry and interference medium having aninfrared (IR) signature, the dropping device comprising: a magazinehaving a feed-out opening directed rearwards with respect to a motionaldirection of the dropping device, wherein a plurality of packs of theinterference medium are arranged sequentially within the magazine; and afeed device comprising rotary members which, on receipt of a feedcommand, stepwise feeds each of the plurality of packs of interferencemedium towards the feed-out opening, said rotary members each includinga camshaft, wherein a number of stop positions of the camshaft is equalto a number of cams on the camshaft, wherein, when the camshaft is inone of the stop positions, a radial outer periphery of one of the camsacts as a stop for feed-out of a next interference medium pack, wherein,when the camshaft is in motion, a front flank of said one of the cams,in a motional direction of the camshaft, acts both as a separationmember between successive interference medium packs and as anacceleration member for a front interference medium pack when the frontinterference medium pack leaves the feed-out opening, wherein eachcamshaft is arranged parallel-driven along at least two opposite sideedges of the feed-out opening, wherein the camshaft included in each ofthe rotary members is mechanically coupled at least through anintermediate gear unit to a belt-driven gear train, said mechanicalcoupling preventing an uncontrolled exit of the next interference mediumpack from the feed-out opening when a belt in the belt-driven gear trainis broken, and wherein a motion of each of the camshafts is stepped upby a number of whole multiples relative to the motion of the feeddevice.
 2. The airborne dropping device of claim 1, wherein the feeddevice further comprises: a feed ram driven by two parallel-runningrunning drive belts fastened at respective ends thereof to a front andrear edge of the ram, wherein said parallel-running drive belts runfirst along respective sides of the plurality of packs of interferencemedium and, second, run back over respective plural diverting wheelsdisposed in a front and rear part of the magazine, respectively, whereinthe rear diverting wheels are driven by the drive belts which, onreceipt of said feed command, produces a stepwise feeding of the ram andthe plurality of packs of interference medium, wherein the reardiverting wheels are further coupled by the intermediate gear unit to arespective camshaft, wherein the number of cams n on the respectivecamshaft is n>1, and a feed-out of the next pack of interference mediumresults from a 1/n fractional turn of the camshaft.
 3. The airbornedropping device of claim 2, wherein n=3 and each of said three cams hassaid radial outer periphery, wherein, when the camshaft is in any one ofsaid stop positions, an associated one of the three cams locks afeed-out of any additional packs of interference medium, wherein, whenthe camshaft is in motion, an associated front flank edge in saidmotional direction of the camshaft first separates the frontinterference medium pack from the next interference medium pack, andthen accelerates the feed-out of said front interference medium pack. 4.The airborne dropping device of claim 1, wherein the stepwise feeding ofeach of the plurality of packs of interference medium by the feed deviceis accomplished by a mechanical connection, the mechanical connectioncomprising: a motor having a motor shaft connected thereto; a drive drumhaving an inner periphery containing grooves thereon, wherein the drivedrum is concentrically arranged around the motor shaft and is driven bythe motor shaft; a driver which contacts at least one of the grooves onthe inner periphery of the drive drum, wherein the driver is removedfrom contact with the grooves after a full turn of the motor shaft; anda second indexing shaft arranged axially and concentrically about themotor shaft along an extension of the motor shaft, the second indexingshaft being coupled to the driver and completely detached from the motorshaft, wherein a rotation of the second indexing shaft is used to drivethe feed-out of the packs of interference medium.
 5. An airbornedropping device for distributing interference medium includingelectronic raspberry and interference medium having an infrared (IR)signature, the dropping device comprising: a magazine having a feed-outopening directed rearwards with respect to a motional direction of thedropping device, wherein a plurality of packs of the interference mediumare arranged sequentially within the magazine; and a feed devicecomprising rotary members which, on receipt of a feed command, stepwisefeeds each of the plurality of packs of interference medium towards thefeed-out opening, said rotary members each including a camshaft, whereina number of stop positions of the camshaft is equal to a number of camson the camshaft, wherein, when the camshaft is in one of the stoppositions, a radial outer periphery of one of the cams acts as a stopfor feed-out of a next interference medium pack, wherein, when thecamshaft is in motion, a front flank of said one of the cams, in amotional direction of the camshaft, acts both as a separation memberbetween successive interference medium packs and as an accelerationmember for a front interference medium pack when the front interferencemedium pack leaves the feed-out opening, wherein the camshaft includedin each of the rotary members is mechanically coupled to the feed deviceof the magazine and is arranged parallel-driven along at least twoopposite side edges of the feed-out opening, wherein a motion of each ofthe camshafts is stepped up by a number of whole multiples relative tothe motion of the feed device, wherein the stepwise feeding of said ramand the plurality of packs of interference medium by the feed device isaccomplished by a mechanical connection including a motor having a motorshaft connected thereto; a drive drum having an inner peripherycontaining grooves thereon, wherein the drive drum is concentricallyarranged around the motor shaft and is driven by the motor shaft; adriver which contacts at least one of the grooves on the inner peripheryof the drive drum, wherein the driver is removed from contact with thegrooves after a full turn of the motor shaft; and a second indexingshaft arranged axially and concentrically about the motor shaft along anextension of the motor shaft, the second indexing shaft being coupled tothe driver and completely detached from the motor shaft, wherein arotation of the second indexing shaft is used to drive the feed-out ofthe packs of interference medium, wherein, between the drive drum andthe output shaft to which the driver is connected is a space in which afixed stop lug for the driver and an eccentric movable about a fixedshaft are disposed, said eccentric being arranged to transfer the driverfrom a first locking position, in which said driver bears with one endedge thereof against the stop lug, into a second active position inwhich a portion of the driver protruding into the drive drum isconnected against the at least one of the grooves on the inner peripheryof the drive drum.
 6. The airborne dropping device of claim 5, furthercomprising: a control command system that starts the motor and drivesthe drive drum when an order is given for the launch of one of theplurality of interference medium packs, wherein, after the motor hasreached an operational speed, the control command system connects thedriver to the inner periphery of the drive drum via the eccentric,wherein the eccentric is returned to a starting position afterconnection of the driver to the inner periphery, wherein, after onerotation of the driver, the eccentric reconnects the driver to the innerperiphery of the drive drum at a different position on the innerperiphery.
 7. The airborne dropping device of claim 2, wherein thestepwise feeding of said feed ram and the plurality of packs ofinterference medium by the rear diverting wheels and the camshafts isaccomplished by a mechanical connection, the mechanical connectioncomprising: a motor having a motor shaft connected thereto; a drive drumhaving an inner periphery containing grooves thereon, wherein the drivedrum is concentrically arranged around the motor shaft and is driven bythe motor shaft; a driver which contacts at least one of the grooves onthe inner periphery of the drive drum, wherein the driver is removedfrom contact with the grooves after a full turn of the motor shaft; anda second indexing shaft arranged axially and concentrically about themotor shaft along an extension of the motor shaft, the second indexingshaft being coupled to the driver and completely detached from the motorshaft, wherein a rotation of the second indexing shaft is used to drivethe feed-out of the packs of interference medium.
 8. Dropping deviceaccording to claim 3, wherein the stepwise feeding of said feed ram andthe plurality of packs of interference medium by the rear divertingwheels and the camshafts is accomplished by a mechanical connection, themechanical connection comprising: a motor having a motor shaft connectedthereto; a drive drum having an inner periphery containing groovesthereon, wherein the drive drum is concentrically arranged around themotor shaft and is driven by the motor shaft; a driver which contacts atleast one of the grooves on the inner periphery of the drive drum,wherein the driver is removed from contact with the grooves after a fullturn of the motor shaft; and a second indexing shaft arranged axiallyand concentrically about the motor shaft along an extension of the motorshaft, the second indexing shaft being coupled to the driver andcompletely detached from the motor shaft, wherein a rotation of thesecond indexing shaft is used to drive the feed-out of the packs ofinterference medium.
 9. A dropping device for distributing aninterference medium, the dropping device comprising: a magazine having afeed-out opening directed rearwards with respect to a motional directionof the dropping device, wherein a plurality of packs of the interferencemedium are arranged sequentially within the magazine; and feed meansincluding an intermediate gear unit coupled to a belt-driven gear trainfor stepwise feeding each of the plurality of packs of interferencemedium towards the feed-out opening, wherein, when the dropping deviceis in a stop position, the feed means for stepwise feeding stops afeed-out of a next interference medium pack, wherein, when the droppingdevice is in a feed position, the feed means for stepwise feedingaccelerates a front interference medium pack when the front interferencemedium pack leaves the feed-out opening, and wherein the feed means forstepwise feeding prevents an uncontrolled exit of the next interferencemedium pack from the feed-out opening when a belt in the belt-drivengear train is broken.
 10. The dropping device of claim 9, wherein thefeed means includes plural camshafts, wherein a motion of each of thecamshafts is stepped up by a number of whole multiples relative to amotion of the feed device.
 11. A dropping device for distributing aninterference medium, the dropping device comprising: a magazine having afeed-out opening directed rearwards with respect to a motional directionof the dropping device, wherein a plurality of packs of the interferencemedium are arranged sequentially within the magazine; a clutch assemblyincluding a drive drum and an output shaft to which a driver isselectively coupled; and indexing means for controlling the feed-out ofthe sequentially arranged packs of the interference medium, wherein theindexing means includes a fixed stop lug cooperating with the driver tostop a rotation of the output shaft, and an eccentric movable about afixed shaft which engages the driver with the drive drum to turn theoutput shaft and feed a front pack of the interference medium.